Stanley and Wilson: Fish abundance near oil and gas platforms 



157 



colonized at the start of the study and we were sam- 

 pling after species stabilization occurred. The latter ex- 

 planation seems most likely, because the age of plat- 

 forms in our study ranged from 8 months to 30 years, 

 and full colonization of artificial reefs in the northern 

 Gulf of Mexico can occur in as little as 15 months 

 (Lukens 1981). 



Seasonal variation Season was an important factor 

 affecting the abundances of fish around oil and gas plat- 

 forms. Smith (1979) and Lukens (1981) reported large 

 fluctuations in species composition and abundance 

 around natural and artificial reefs in the northern Gulf 

 of Mexico, and based on our results this would include 

 fish populations around oil and gas platforms off the 

 Louisiana coast. 



The apparent higher abundances of spotted seatrout 

 in the spring and summer may be a result of a tem- 

 perature-induced increase in feeding rate and/or the 

 aggregation of the fish into spawning schools (Johnson 

 and Seaman 1982). 



The increase in pelagic fish catches from winter 

 through fall indicated that abundance may have been 

 related to water temperature. This is consistent with 

 the findings by Fable et al. (1981), as they found that 

 the charterboat catches of king mackerel and other 

 pelagic species in the northeast Gulf of Mexico in- 

 creased with water temperature. 



Lassuy (1983) reported that Atlantic croaker abun- 

 dance was highest in the spring and summer, while Sut- 

 ter and Mcllwain (1982) reported silver/ sand seatrout 

 abundance to be highest in the winter and spring. This 

 may explain the apparent conflicts in the results from 

 the MRA with respect to seasonal abundances of these 

 two species. Silver/sand seatrout may have been abun- 

 dant in the winter and spring, and Atlantic croaker in 

 the spring and summer. However, when these species 

 were grouped the seasonal abundance results explained 

 only silver/sand seatrout and not the entire group. 



Our results, along with those of others (Gallaway et 

 al. 1981b, Reagan 1982) provided evidence that bluefish 

 and red drum were seasonal transients with highest 

 abundances from fall through spring. Shark and cobia 

 abundances appeared to be highest in the spring and 

 decreased thereafter. 



Angler characteristic variables Overall, fishing power 

 was not equal because fishermen with larger vessels 

 and engines had access to deeper water, and fishermen 

 with sophisticated electronics could more easily locate 

 fish. Because reef fish, Atlantic croaker, and silver/ 

 sand seatrout are found in deep water, anglers with 

 large vessels and engines had the highest catches for 

 these species, while cobia, sharks, and pelagic species 

 were more frequently caught by vessels having sophis- 



ticated electronics. Since spotted seatrout were found 

 in shallow water, large vessels or sophisticated elec- 

 tronics did not increase spotted seatrout catches. 



Geological and meteorological variables Geological 

 and meteorological variables were not significant pre- 

 dictors of fish abundance around oil and gas platforms. 

 Meteorological variables were probably not important 

 because fishermen generally fish only in good weather, 

 consequently catch rates during poor weather condi- 

 tions were not reported. 



Conclusions 



The physical construction of oil and gas platforms 

 precludes sampling of the associated sportfish popula- 

 tions using traditional methods (e.g., gillnets, trawls). 

 Based on the results of this logbook program, the col- 

 lection of CPUE data over long periods of time may 

 be an effective technique of monitoring the fish popula- 

 tions susceptible to angling associated with artificial 

 reefs. Although the data supplied by the logbooks is 

 an index of relative abundance of fish susceptible to 

 angling and is biased towards larger individuals, it pro- 

 vides a valuable source of data which is otherwise dif- 

 ficult to obtain. 



With the advent of the "Rigs to Reefs" initiative in 

 Louisiana, biological criteria to determine where to 

 locate retired oil and gas platforms as artificial reefs 

 was needed. Information derived from this study sug- 

 gests that optimal artificial reef configurations exist, 

 but vary depending on the species. To effectively site 

 artificial reefs for reef fish, Atlantic croaker, and 

 silver/sand seatrout there should be large complex plat- 

 forms at intermediate depths; for pelagic species ar- 

 tificial reef size is not a factor, although they should 

 again be placed at intermediate depths. Optimal siting 

 of artificial reefs for spotted seatrout should include 

 small structures in shallow water. Gallaway and Lewbel 

 (1982) suggested that abundances of some species were 

 directly proportional to the submerged surface area of 

 oil and gas platforms. We believe that the relationship 

 between fish abundances and artificial reefs is much 

 more complex, with other factors, such as natural and 

 temporal variability of species distribution and abun- 

 dance interacting with physical platform variables and 

 water depth to determine overall species abundances. 



Acknowledgments 



The authors thank the 55 anglers and 10 charterboat 

 operators for maintaining logbooks; the oil and gas 

 operators for providing information and drawings on 



